Glucose transport into the rat sciatic nerve from blood, across blood vessels of the nerve endoneurium, is by a facilitated transport system that demonstrates stereospecificity and saturation, and allows matching of transport and nerve metabolism. The permeabilities of nerve capillaries and of the perineurium to ions are low, but do not demonstrate active or regulated transport of ions. Calcium is not transported at the perineurium of frog nerve, but is accumulated by perineurial cells. Blood flow in the nerve of the anesthetized rat was measured continuously by laser Doppler flowmetry, and shown to be proportional to flow as measured with 14C-iodoantipyrine at discrete times. Autoradiography demonstrated heterogeneous flow distribution within the nerve. Endoneurial blood vessels of the frog sciatic nerve remained intact during normal rates of perfusion, but were damaged by hypertension. Vesicular profiles could be demonstrated in the perineurium of frog nerve and in endothelial cells of pial blood vessels, using rapid freezing and freeze-substitution. These tissues are diffusion barriers, so that the profiles do not contribute to transcellular channel-mediated or vesicular transport. Alkaline phosphatase was distributed in some vesicles, suggesting that they are microdomains for enzyme activity.